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03-01-2011, 09:17 AM   #1
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Zoom/Power zoom on flashes: why?

Another doofus newbie question:

What does a zoom on a flash do? Do you, or why do you, need a power zoom to do it?

I'm looking at Bower/Rokinon/Etc. clones (yes, I've read Matt's section but I'm even more lost now...)

Thanks,
hray

03-01-2011, 09:42 AM   #2
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The flash with zoom is likened to a zoom lens too but being light it travels only so far.
The power zoom (flash) syncs with the lens focal length you choose.
If you have set the zoom lens on wide, the flash has a motor that retracts the zoom to wide so the light is more scattered and would illuminate a wider area.
Zoom the lens to a higher telephoto setting and the flash motor zooms in (usually around 85mm) to match the focal length you chose and would provide a more focused beam on your farther subject.
Mind you though that these flashes have also only a certain flash output (GN #) and if you have a very powerful zoom lens, even if the flash also zooms, it might not be able to light that subject...so, this should be used also within reason.
Another thing, these flashes with power zoom will work in-sync only with AF lenses.
If you got manual lenses, be it zoom or not (even telephoto), you can/have to set the flash zoom manually.
03-01-2011, 09:49 AM   #3
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The zoom on a flash concentrates the light more when at e.g 48mm than at e.g. 16mm. So with a lowish guide number (GN) you can still have a longer 'reach'. Why not always use it at the longest position? Because the light beam becomes narrower and therefore part of the subject will not 'receive' light when using a lens with a shorter focal length resulting in an image that is dark at the edges.

From the Metz 48 AF-1 manual:
at 18mm GN is 21, at 50mm GN is 35 and at 105mm GN is 48

The 'real' GN of this flash is 35 although the type number implies 48; just marketing. Same for the Pentax AF540 (implied 54, 'real' 45).
03-01-2011, 09:52 AM   #4
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We have a review of this on the accessories section.
Search for the Vivitar DF 383 review.
You can also got to overstock.com and see some of the reviews: Bower AF Pentax/ Samsung Digital SLR Camera Flash | Overstock.com
That is where I bought mine and the first review is mine too!
They have the Rokinon and Vivitar but is the same potato.
I wanted the Vivitar or Rokinon but the Bower was priced lower so I went for the Bower. Why should I pay more for the same thing with just a different branding??

03-01-2011, 11:01 AM   #5
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Not to repeat what has been presented by others above but the zoom function is more than just "extending the reach.

any lens has a specific ffield of view, measured in degrees.

the flash has a field of projection of light, also in degrees, but having to work all this out is difficult, so lenses are referred to in terms of focal lenght, and the flash reports the equivelent "focal length" that corresponds to your lenses field of view.

Zoom out, and the flash widens the field if illumination , zoom in and the flash narrows the field of illumination.

it does this so you get correct and uniform coverage, especially at the wide end, and by narrowing the field of view, gives you more illumination at the long end of the focal length range.

if you shoot with the wrong focal length on the flash, you risk getting dark edges (flash FL too long for the field of view of the lens) or waste light by illuminating things not in the field of voiew for the lens.
03-01-2011, 11:38 AM   #6
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Zoom on a flash is a gimmick - it's basically a sleeve that moves a fresnel lens in front of the flash head to disperse or concentrate the flash output - a flash specialist might utilize it some but for the rest of us not too useful. I have a Canon 300TL from my film days which has manual zoom setting for four focal lengths; 24, 35, 50 and 85mm. Not exactly extreme focal length on the telephoto end. I just left the flash at 24mm setting and placed a diffuser in front of it to achieve more even lighting and let the TTL flash metering take care of the exposure. Btw, placing a diffuser in front of the flash more or less negates the zoom feature anyways.
03-01-2011, 08:12 PM   #7
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Thanks, everyone; in my K1000 film days, I had a Zykkor 355 "computerized" flash that had a couple sliders, for ISO and f/stop values, but I never saw that they actually did anything. I just put the diffuser on for anything within 10' (99% of my shots) and bounced the light off the ceiling...

Sounds like my needs would be met with a minimalist flash like the Bower. (Sheesh...TTL flash adjustment, and I'm calling it "minimalist!" Never even considered that was possible in the early 80s when I got my K1000!!)
03-02-2011, 10:53 AM   #8
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You'll like it.
As an affordable flash with features of the OEM except for the wireless control, it is great!
Has a built in pull-out diffuser too much like the Canon OEM flashes, so you don't need to buy other diffusers/thing-a-ma-jigs..
..oh yeah, it's P-TTL too ang not just TT-L..meaning compatibility with the new system.

03-03-2011, 02:36 PM   #9
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Addition there: It's a nice little convenience I don't happen to care about cause, well, to me, it's not a big deal, and it's also just one more thing to possibly break. But that probably won't be a big deal, either.

Basically, I suppose it's a nice convenience, and might save some flash power/extend your range, a little, but you can live without it. Wouldn't choose a unit based on its presence or absence, though.
03-03-2011, 02:44 PM   #10
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I suppose it is not terribly useful with bounce flash which (to me) is the point of an external flash pretty much (as things look less like a documentary from an h-bomb test ).
03-03-2011, 02:58 PM   #11
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QuoteOriginally posted by jolepp Quote
as things look less like a documentary from an h-bomb test
03-03-2011, 03:02 PM   #12
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QuoteOriginally posted by jolepp Quote
I suppose it is not terribly useful with bounce flash which (to me) is the point of an external flash pretty much (as things look less like a documentary from an h-bomb test ).
That's a point in favor of the manuals, I suppose: I'll manually zoom my new little guy for bouncing out of habit unless the ceiling's low or something. I didn't often bother with my big ol Vivitar 285, most of the time, but that was always enough power.

Playing with my little Metz 36 seems to actually give pretty even (if not a little flat, actually) results with a cheapie diffuser sock thing I got with some stuff from Hong Kong, of all things. (I forget why I bought it in the first place, but it was like a buck ) For that, I can zoom it out manually pretty handily for a bit more directionality, actually.

Anyway, manual zoom heads aren't all bad, poster. Likely you won't be worrying either way for a while.
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